Keywords:

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species. Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape. Their keystone status is attributed primarily to the effects of their burrowing and foraging behavior, but they differ ecologically in several important respects. We studied the comparative functional roles of these species where they co-occur at the Sevilleta National Wildlife Refuge, New Mexico, focusing on their impacts on grassland vegetation, lizard communities, and ground-dwelling arthropod and grasshopper communities. We evaluated the impacts of these rodents on vegetation and animal communities in areas where prairie dogs and kangaroo rats co-occurred compared to areas where each rodent species occurred alone. We found that vegetation cover, structure, and species richness varied across a gradient extending out from the mound centers, and these patterns differed between prairie dog and kangaroo rat mounds. Certain species and functional groups of plants associated differentially with mounds and landscape patches occupied by prairie dogs and banner-tailed kangaroo rats. Where both species co-occurred locally there was greater soil disturbance, more organic material from their feces, and higher activity of other animals. The overall effect of these rodents was to create a mosaic of different patches across the landscape such that their combined activities increased andscape heterogeneity and plant and animal species richness. Our results also demonstrated that prairie dogs and kangaroo rats have keystone-level impacts on lizard communities. Their burrow systems provided important habitats for multiple lizard species, especially the lesser earless lizard (Holbrookia maculata). At the landscape-scale, the total number of lizards was two-times greater on the mounds where both prairie dogs and banner-tailed kangaroo rats co-occurred than where only kangaroo rats occurred. Prairie dogs and kangaroo rats were also found to have keystone-level impacts on arthropod communities. Their burrow systems provided important habitats for multiple trophic and taxonomic groups of arthropods, and increased overall arthropod abundance and species richness on the landscape. Many arthropods also were attracted to the aboveground habitats around the mounds and across the landscapes where the rodents occurred. Detritivores, predators, ants, grasshoppers, and rare rodent burrow inhabitants showed the strongest responses to prairie dog and kangaroo rat activity. The impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of arthropods. Our results demonstrated the complementary effects of two co-occurring keystone species on their associated biotic communities.